1. Field of Invention
This invention relates to a method for enhanced sanitation and oxidation of aqueous solutions at aquatic facilities.
2. Background of the Technology
Aqueous system that are exposed to various forms of oxidant demand as well as introduction of microbiological contamination must be effectively treated to control transfer of disease such as in the case of a swimming pool and fouling such as in the case of an industrial cooling system.
Chlorine dioxide has been proven very effective at inactivating microbiological organisms in such applications. However, generating chlorine dioxide can be hazardous due to the explosive nature of the gas as well as the potential for human exposure to toxic concentrations. Furthermore, chlorite anion concentrations must be held to a minimum in water that may be consumed due to toxicity concerns. The U.S. EPA has put a limit in drinking water at 1.0 ppm as chlorite anion.
Chlorine dioxide is typically produced in a chlorine dioxide generator where either acid or chlorine are combined with a chlorite donor to generate chlorine dioxide. In order to achieve efficient conversion of chlorite to chlorine dioxide, high concentrations are reacted thereby generating a high concentration of gas which is potentially dangerous.
Chlorine dioxide is also produced by forming tablets from reactive components such as dichloroisocynauric acid and sodium chlorite or an acid source and sodium chlorite. These also have limitations and also have the concern of producing chlorine dioxide gas premature to the application due to exposure to relative humidity.
Regardless of these efforts to efficiently and safely produce chlorine dioxide, the efficiency of chlorite conversion from tablets is commonly less than 70%, and the hazards of producing concentrated solutions remains. In the case of reacting liquid forms of acid and sodium chlorite, the low pH of the solution requires neutralization.
Using these methods of chlorine dioxide generation also waste considerable amounts of reagents such as chlorite as well as elevate cost due to the inability to regenerate the chlorite ions that result from the reduction of the chlorine dioxide back to chlorite or the residual chlorite that was not activated during the initial formation of chlorine dioxide.
3. Prior Art
U.S. Pat. No. 5,603,840 comprises adding bromide to a cooling water system containing corrosion and scale control treatment chemicals at elevated concentrations (40 ppm or greater). A fraction of the recirculating water is drawn off in a side stream and ozonated. Ozone oxidizes bromide to bromine which then serves as a biocide. The bromide levels are chosen such that the ozone/bromide reaction is preferred over the ozone/treatment chemicals reaction. Thus, the addition of bromide at elevated concentrations, while acting as a biocide precursor, serves to protect treatment chemicals necessary for corrosion and scale control.
Publication No. WO2007/078838 A2 discloses a solid composition comprising a solid source of hypobromous acid and a solid source of chlorite to produce chlorine dioxide. The composition has a pH of 5-9 at 25° C. when dissolved at a concentration of 1 gram per 100 ml water.
Publication No. U.S. 20030080317 discloses a massive body that uses chlorine, an acid and chlorite to produce chlorine dioxide.
U.S. Pat. No. 6,303,038 discloses a water soluble dialkylhydantoin and a source of bromide ion are added to a body of water needing sanitization. This is followed by contacting the body of water with an oxidizing agent, which creates biocidal species in situ in the body of water.
4Discussion of Prior Art
The tablet technologies disclosed in Publication No. WO2007/078838 A2 and Publication No. U.S. 2003/0080317 clearly illustrate thru the examples provided the inability to produce a solution substantially free of chlorite, even when utilizing a system that provides a high concentration of reactants to maximize efficiency of the chlorite conversion.
The application of chlorine dioxide using these prior art methods lends itself to the potential accumulation of chlorite anions when applied to recirculating aqueous systems. This is the result of the prior arts inability to effectively achieve near 100% conversion of chlorite anion to chlorine dioxide in the resulting solution, and has no provision for effectively regenerating chlorite anions resulting form the reduction of chlorine dioxide once the solution is applied to the said aqueous system. Therefore chlorite anions will accumulate.
Since many applications limit the amount of chlorite anion that can be present in the water, it is desirable be able to limit the accumulation to levels to less than about 1.0 ppm as ClO2−. This criteria would therefore substantially limit or altogether prohibit the use of chlorine dioxide generated by these prior art methods in such systems.
In order to sustain chlorine dioxide concentrations without accumulating chlorite anions above about 1.0 ppm as ClO2−, regeneration of a dilute solution comprising chlorite anions back to chlorine dioxide under the conditions of the aqueous system is required.
However, in some applications such as poultry washing systems or laundry washing machine wash water where excess chlorite maybe acceptable, it will be desirable to safely and efficiently sustain a desired concentration of chlorine dioxide to enhance disinfection in the case of the poultry washing and oxidation along with disinfection in the case of washing machine wash water. The cyclic process of the invention provides a means of safely generating and sustaining the desired concentration of chlorine dioxide in such applications, without the need for special handling since the chlorine dioxide is produced in dilute solution in-situ to the application. Concern of tablet dissolution to prevent bleaching of laundry etc can be effectively eliminated since the chlorine dioxide is produced after being dispersed wash water. The potential for localized high concentrations in averted.
Also, the need for continued replenishment of chlorine dioxide solution from the tablet or methods using generators is altogether eliminated since surrogate anions of chlorine dioxide and hypobromous acid are regenerated in the process back to their respective oxyhalogen's. Only enough supplemental supply of bromide and chlorite anions is required to sustain the cyclic process. Tremendous cost saving, simplicity in operation, and safety are significant benefits.